This invention relates to a flexible disk drive and a flexible disk assembly used as a recording medium for writing and reading data in a flexible disk device. It is important to use a flexible disk within specified temperature and humidity ranges to maintain its compatibility and not to cause a deterioration of the magnetic characteristics. Therefore, standards for a flexible disk assembly have been established both in Japan and other countries. Nevertheless, conventionally, when a flexible disk is set in a flexible disk device, writing or reading of data is performed regardless of the temperature and humidity of the surrounding environment.
A global standard for comparatibility of flexible disks is established by ISO (International Organization for Standardization), and other standards are based on this global standard, which include JIS (Japanese Industrial Standards) in Japan, ANSI (American National Standards Institute) in the U.S., and ECMA (European Computer Manufacturers Association) in Europe.
Flexible disk assemblies of 8-inch and 5.25-inch sizes have soft plastic jackets. The material of the jackets is normally a vinyl chloride-based resin. Therefore, when the temperature of the jacket surface exceeds about 53.degree. C., there is a fear that the jacket will be deformed permanently. For 3.5-inch flexible disk assemblies, hard cases of ABS (acrylonitrile butadiene styrene copolymer) resin or the like are used, and therefore, the allowable temperature is relatively high. However, when a flexible disk assembly of this type is used in a flexible disk device, if a flexible disk in the assembly is subjected to stress and exposed to a temperature of higher than 60.degree. C., the disk itself is likely to soften, because the disk is made chiefly of PET (polyethylene terephthalate). Thus, for those flexible disk assemblies the temperature upper limit is specified at 59.degree. C. On the other hand, a magnetic sheet of the flexible disk is made of an about 75 .mu.m-thick base material coated on both sides with a magnetic layer of several .mu.m. So, the expansion and contraction coefficients of the magnetic sheet due to changes in temperature and humidity are governed by the coefficients of the base material. The ISO standard provides the thermal expansion coefficient and the humidity expansion coefficient of a flexible disk by the following formulas (1) and (2). EQU .alpha..sub.T =(17.+-.8).times.10.sup.-6 mm/mm/.degree.C. (1) EQU .alpha..sub.H =(0.about.15).times.10.sup.-6 mm/mm/% RH (2)
The expansion and contraction of a flexible disk are large and may easily lead to malfunctioning by off tracking. The ISO standard specifies the upper limit of wet-bulb temperature at 29.degree. C. (and 26.5.degree. C.). The relationship between the allowable temperature and humidity for a flexible disk assembly is shown in FIG. 6. The hatched area in FIG. 6 indicates the allowable working environment of a flexible disk assembly. Therefore, it is difficult to exchange data outside the allowable environmental range.
However, when a conventional flexible disk assembly as mentioned above is used in a low-temperature region, such as in cold districts, or conversely, when it is used at high temperature in midsummer, the flexible disk assembly is often loaded in a flexible disk device to write or read data in an inadequate environment having a temperature and humidity exceeding the allowable ranges. Therefore, problems may occur, such as an abnormal operation of the device, a deterioration in the magnetic characteristics of the magnetic disk sheet, and a compatibility error in writing or reading data. Even if a flexible disk device or a system incorporating a flexible disk device is located in the user's office room and in an allowable working environment for the flexible disk assembly, but the temperature and humidity of the place where the flexible disk assembly has been stored or the temperature and humidity of the flexible disk assembly itself are not within the allowable ranges, a deterioration of the magnetic characteristics or a compatibility error as mentioned above will occur when the flexible disk assembly is loaded immediately after it is taken out of storage. Another problem is that it is difficult for the user to check if the flexible disk assembly is at allowable temperature and humidity for its use.